I. Field of the Invention
This invention relates in general to complex metal hydrides and their synthesis, and in particular to a process which permits production of sodium aluminum tetrahydride at relatively moderate pressure.
II. Description of the Prior Art
Various processes have been proposed for making alkali metal aluminum hydrides in both hydrocarbon and other solvents from alkali metal hydrides and from the elements.
Several processes are known for the production of complex metal hydrides in ether solvents. The use of ether solvents has many disadvantages however. Sodium aluminum tetrahydride tends to undergo dangerous thermal decomposition in ethers like tetrahydrofuran (THF), the dimethyl ether of ethylene glycol (monoglyme), or the dimethyl ether of diethyleneglycol (diglyme).
The commercial grade ethers must be purified to remove water, alcohols, and explosive peroxides and hydroperoxides before use. Also, long-term storage of ether permits deterioration (ether cleavage) which affects reactions in which it is used. Finally, besides the inherent danger of ethers, their cost is much greater than hydrocarbon solvents which are innocuous to the reaction of the present invention.
Efficient process to make sodium aluminum tetrahydride at very high pressures of 2000 psig or more have been developed. There exists a need however for an economical process with relatively rapid throughput at relatively moderate pressures.
If the production of hydrides can be achieved at moderate reaction pressures, then the process is made available (a) to locations where higher pressures are not permitted; (b) in less expensive equipment adapted only for moderate pressure limits; and (c) in older equipment which, though previously rated for high pressures, is currently because of wear or age suitable for only moderate pressures.
The alkali metal aluminum tetrahydrides, including sodium aluminum tetrahydride, are well known reducing agents for chemical synthesis and have other utilities well known to those skilled in the art. The alkali metal aluminum tetrahydrides may also be used to reaction with various silicon-containing compounds to produce precursors to high purity silicon, e.g. silane. The production of sodium aluminum tetrahydride is quite small and there is only one major producer in the world.